i know few things that you houdlnt do while eating in japan or infront of a japanese person:

-Don't poke food with the tip of your chopstick.
-Dont lick your chopstick tip.
-you should not point to other people with a chopstick.
-you should not eat directly from the main dish but take some of the food place them in your dish or bowl and then eat.
-dont make noises whle eating with a chopstick , like hitting them together and such.

japanese food typically isn't spicy. if you find anything with curry in it, that's likely to be spicy...but japanese curry certainly isn't one of the hotter curries out there.

manners... well, I've heard that you shouldn't stick your chopsticks straight up in your rice (as it imitates incense), put them in a V form (also imitating incense), or cross them. just put them side-by-side. and I think this is a given anywhere - but don't drum with your chopsticks.